suggest that oxygen levels in the deep ocean didn't reach modern levels until 140 million years after the Cambrian explosion, in the Devonian period. "From a global perspective, we didn't see the ...

3 min read The Cambrian period ... It may be that oxygen in the atmosphere, thanks to emissions from photosynthesizing cyanobacteria and algae, were at levels needed to fuel the growth of more ...

All animal evolution for the last half billion years has come from tinkering with these Cambrian body plans ... Some point to the increase in oxygen that began around 700 million years ago ...

At about 2.4 billion years ago, oxygen was released from the seas as a byproduct of photosynthesis by cyanobacteria. Levels of the gas gradually climbed, reaching about one percent around two ...